/*
 * hc-sr04.c
 *
 * Copyright 2022 dh33ex <dh33ex@riseup.net>
 *
 * This program is free software; you can redistribute it and/or modify
 * it under the terms of the GNU General Public License as published by
 * the Free Software Foundation; either version 3 of the License, or
 * (at your option) any later version.
 *
 * This program is distributed in the hope that it will be useful,
 * but WITHOUT ANY WARRANTY; without even the implied warranty of
 * MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the
 * GNU General Public License for more details.
 *
 * You should have received a copy of the GNU General Public License
 * along with this program; if not, write to the Free Software
 * Foundation, Inc., 51 Franklin Street, Fifth Floor, Boston,
 * MA 02110-1301, USA or see <http://www.gnu.org/licenses/>.
 *
 *
 */

#ifndef __msp430_h_
    #include <msp430.h>
#endif
#include "hc-sr04.h"


void HC_SR04_init(unsigned char trig, unsigned char echo) {
    /* setup ports */
    P1DIR |= trig;              /* set TRIGER to output */
    P1OUT &= ~trig;             /* clear TRIGER port initially */

    P1DIR &= ~echo;             /* set ECHO to input */
    P1REN &= ~echo;             /* disable resistor */

    /* setup timer */
    TA0CTL |= TACLR;            /* reset timer */
    TA0CTL |= MC_2;             /* continuous mode */
    TA0CTL |= TASSEL_2;         /* choose SCMLK */
    TA0CTL |= ID_0;             /* div-by-1 in prescalar */
}


float HC_SR04_mesure(unsigned char trig, unsigned char echo) {
    float distatnce;
    P1OUT |= trig;
    __delay_cycles(15);
    P1OUT &= ~trig;
    TA0R = 0;
    while (!(P1IN & echo)) {
        if (TA0R > 16384) {     /* timeout */
            return -1;
        }
    }
    TA0R = 0;
    while (P1IN & echo);
    distatnce = TA0R * 0.017;
    return distatnce;
}
